Thermal airflow sensors have conventionally been a mainstream airflow sensor that is installed in the intake air passage of internal combustion engines, such as those of automobiles, to measure intake air volume since the thermal airflow sensors are capable of directly detecting amount of air.
Recently, there has been developed an airflow sensor formed by having resistors and insulating layer films deposited on a silicon substrate by use of semiconductor micromachining technology, part of the silicon substrate being removed thereafter by a solvent represented by KOH to form a thin-wall portion. This airflow sensor is drawing attention because it has high-speed responsiveness and is capable of detecting counter flows thanks to its quick response. In recent years, for the purpose of reducing the number of components constituting the substrate portion (printed substrate, silicon substrate, etc.), study has been underway to form a structure in which this airflow sensor is mounted on a lead frame of which the periphery is molded in resin.